The invention relates to an apparatus for reading and/or writing information from/on a recording medium, comprising a scan element for scanning the medium and a servo loop for positioning said scan element, said servo loop comprising
an actuator for driving the scan element, said actuator comprising an actuator coil and PA1 a control means conceived to feed the actuator coil with a drive current dependent on a position signal which is indicative of the actual position of the scan element and a reference signal which is indicative of the desired position of the scan element. PA1 the apparatus comprises an inductance influencing means to vary the inductance of the actuator coil as a function of the position of the scan element and PA1 the control means are conceived to derive the position signal from the actual inductance of the actuator coil.
The invention also relates to an actuator for an apparatus for reading and/or writing information from/on a recording medium, which actuator comprises an actuator coil and a magnetic member.
The invention further relates to a control means for driving an actuator coil in order to position a scan element in an apparatus for reading and/or writing information from/on a recording medium, the control means being conceived to feed the actuator coil with a drive current dependent on a position signal which is indicative of the actual position of the scan element and a reference signal which is indicative of the desired position of the scan element.
Such an apparatus is known from JP-A-08212579. The known apparatus is an optical drive for reading and or writing information on an optical disk. The apparatus comprises an optical head with an objective lens and a so called Solid Immersion Lens (SIL). The objective lens is positioned relative to the disc by means of a first actuator. The SIL is positioned relative to the objective lens by means of a second actuator which is operative between the objective lens and the SIL. In order to derive a position signal indicative of the position of the SIL relative to the objective lens, the capacitance of a capacitor formed by a holder of the SIL and a holder of the objective lens is measured.
The above citations are hereby incorporated in whole by reference.